Early suppression fast response (xe2x80x9cESFRxe2x80x9d) sprinklers are a well known and well defined class of ceiling fire sprinklers. ESFR sprinklers were developed in the 1980""s by Factory Mutual Research Corporation (xe2x80x9cFMxe2x80x9d) with the assistance of certain sprinkler manufacturers in an effort to provide improved fire protection against certain high-challenge fire hazards. According to FM, ESFR sprinklers combine fast response with greater supplied and actually delivered water densities for greater fire suppression capability. Previous sprinklers (standard sprinklers) provided protection by merely keeping such fires under control. Ultimately the initial fuel source would deplete itself or other fire fighting equipment would have to be brought to the scene to extinguish the fire.
The performance requirements of ESFR sprinklers are set forth in Underwriters Laboratories, Inc. (xe2x80x9cULxe2x80x9d) STANDARD FOR EARLY-SUPPRESSION FAST-RESPONSE SPRINKLERS UL 1767. This standard was first published in 1990. Factory Mutual Research Corporation (xe2x80x9cFactory Mutualxe2x80x9d or xe2x80x9cFMxe2x80x9d) also has an Approval Standard For Early Suppressionxe2x80x94Fast Response (ESFR) Automatic Sprinklers, Class Number 2008. The current ESFR standards and all earlier ESFR standards of either organization are incorporated by reference herein in their entirety.
Requirements for the installation and use of ESFR sprinklers are included in various standards of the National Fire Protection Association including the Standard for the Installation of Sprinkler Systems, NFPA 13; the Standard for General Storage, NFPA 231; and the Standard for Rack Storage of Materials, NFPA 231c. The current and earlier editions of these standards to the extent that they pertain to ESFR sprinklers are incorporated by reference herein. Installation and use requirements for ESFR sprinklers are also given Loss Prevention Data sheets 2-2, xe2x80x9cEARLY SUPPRESSION FAST RESPONSE SPRINKLERSxe2x80x9d, Factory Mutual System, Factory Mutual Engineering Corp., 1987, which is also incorporated by reference herein. Loss Prevention Data sheets 2-8 N, xe2x80x9cInstallation of Sprinkler Systemsxe2x80x9d, Factory Mutual System, Factory Mutual Engineering Corp., 1989, presents other installation and use requirements for ESFR and other sprinklers generally which are not presented in Loss Prevention Data sheets 2-2 and is also incorporated herein.
The standards specify the construction, performance, installation and operation of ESFR sprinklers with significant particularity. For example, the discharge coefficient (or xe2x80x9cKxe2x80x9d factor) of an ESFR sprinkler is nominally 14 and must be within the range of 13.5-14.5, where the discharge coefficient is calculated by dividing the flow of water in gallons per minute through the sprinkler by the square root of the pressure of water supplied to the sprinkler in pounds per square inch gauge. Ordinary or standard sprinklers are considered to have response time indices (xe2x80x9cRTIxe2x80x9d) of 100 meterxc2xdsecondxc2xd (xe2x80x9cmxc2xdsecxc2xdxe2x80x9d) or more although the response time indices actually reported for these sprinklers have all exceeded 100 mxc2xdsecxc2xd. One special class of faster operating sprinklers exists with response time indices between 50 and 80 mxc2xdsecxc2xd. Existing ESFR sprinklers must exhibit response time indices of less than 40 mxc2xdsecxc2xd. The installation and use standards further require, among other things, that a minimum operating pressure of 50 psi be provided to ESFR sprinklers.
ESFR sprinklers were originally designed to suppress fires in warehouses with thirty-foot ceilings where flammable stock such as certain plastics is piled up to twenty-five feet high in racks. In many instances, available water supplies are not capable of providing a minimum operating pressure of 50 psi to thirty-foot high sprinklers. In such cases, a supplemental pump is needed to boost water pressure before ESFR sprinklers can be used. The cost of providing an auxiliary pump can be significant. For example, in protecting a 40,000 square foot building with ESFR sprinklers, it is estimated that the cost of providing an auxiliary pump can represent about twenty-five (25) percent of the entire cost of the installed sprinkler system. In certain installations, a second, back-up pump may be needed. If comparable protection might be provided at pressures below the current 50 psig minimum required pressured for ESFR sprinklers, the need for a pump might be avoided. In instances where a pump would be required in any event, lower pressure requirements may permit the use of a lower capacity, less expensive pump or the use of the same pump with smaller diameter, higher friction but less expensive supply lines. Each of these three possible options could provide significant savings in installation costs of ESFR sprinklers.
In one aspect the invention is a low pressure fast response bulb sprinkler comprising a generally tubular body having an inlet end, an opposing discharge end and an internal passageway extending between the inlet and discharge ends with a K factor greater than 16 where the K factor equals the flow of water in gallons per minute through the internal passageway divided by the square root of the pressure of water fed into the internal passageway in pounds per square inch gauge; a deflector coupled with the tubular body and spaced from and generally aligned with the discharge end of the internal passageway so as to be impacted by a flow of water issuing from the discharge end of the passageway upon activation of the sprinkler, the deflector being configured and positioned to deflect the flow of water generally radially outwardly all around the sprinkler; a closure releasably positioned at the discharge end of the tubular body so as to close the internal passageway; and a heat responsive trigger at least including a frangible liquid containing glass bulb mounted to releasably retain the closure at the discharge end of the tubular body, the glass bulb having a response time index of less than 100 meterxc2xdsecxc2xd (mxc2xdsecxc2xd).